Engines may utilize a turbocharger or supercharger to compress ambient air entering the engine in order to increase power. Compression of the air may cause an increase in air temperature, thus, an intercooler or charge air cooler (CAC) may be utilized to cool the heated air thereby increasing its density and further increasing the potential power of the engine. Condensate may form in the CAC when the ambient air temperature decreases, or during humid or rainy weather conditions, where the intake air is cooled below the water dew point temperature. Further, when the charge air entering the CAC is boosted (e.g., an induction pressure and boost pressure are greater than atmospheric pressure), condensate may form if the CAC temperature falls below the dew point temperature. As a result, condensate may collect at the bottom of the CAC, or in the internal passages, and cooling turbulators. When torque is increased, such as during acceleration, increased mass air flow may strip the condensate from the CAC, drawing it into the engine and increasing the likelihood of engine misfire and combustion instability.
Engines may utilize a compressor recirculation valve (CRV) to divert intake air around a compressor of the turbocharger to control an amount of boost provided to an intake manifold of the engine. For example, opening the CRV may reduce boost pressure and induction pressure. One approach to control the boost and/or induction pressure includes actively controlling the CRV. One example approach is shown by Sun et al. in U.S. Pat. No. 8,001,778. Therein, a compressor bypass valve (or CRV) is adjusted in response to exhaust temperature and compressor surge.
However, the inventors herein have recognized potential issue with such systems. As one example, controlling the CRV in this way may cause the CRV to remain closed under conditions when increased boost is not required by a torque demand. As a result, the closed CRV may build up induction pressure before the throttle, thereby increasing a potential for condensate formation in the CAC.
In one example, the issues described above may be addressed by a method for adjusting a compressor recirculation valve (CRV) in an engine to decrease an induction pressure in response to charge air cooler condensate forming conditions. Specifically, a compressor recirculation valve may be opened in response to charge air cooler condensate forming conditions, during driving conditions when the induction pressure is greater than required to produce a manifold pressure required for a torque demand. In one example, condensate forming conditions include an induction pressure greater than atmospheric pressure (e.g., an induction pressure ratio greater than 1). In another example, condensate forming conditions include a humidity greater than a first threshold. After opening the compressor recirculation valve to decrease the induction pressure, the compressor recirculation valve may be closed in response to one or more of the induction pressure decreasing to the atmospheric pressure and/or a requested manifold pressure increasing above the induction pressure. Further, during certain engine operating conditions, a wastegate may be opened in addition to opening the compressor recirculation valve to increase the induction pressure reduction.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.